Lindsay LohanIn Fear of Possible Stalker

12/16/2010 6:00 AM PST BY TMZ STAFF

Lindsay Lohan is afraid she's being targeted by a stalker -- and the threat is so real that people at Betty Ford are taking measures to protect her ... TMZ has learned.

Sources familiar with the situation tell TMZ Lindsay has been receiving harassing phone calls and text messages from unknown numbers -- and the unidentified person behind them has been making disparaging statements about her recovery ... and her family.

Even scarier, the unknown person is saying he/she knows where Lindsay is staying and is watching her.

We're told Betty Ford officials are so concerned, they're moving their most famous patient to a more secure, private facility.

We're also told BF has limited Lindsay's outings out of concern for her safety.